Nuclear magnetic resonance (NMR) spectroscopy is being used to determine the concentrations of very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL) subclasses of different size. These subclasses have unequal associations with coronary heart disease. Nuclear magnetic resonance distinguishes among the subclasses on the basis of slight differences in the spectral properties of the lipids carried within the particles, which vary according to the diameter of the phospholipid shell. Studies using NMR spectroscopy have shown that individuals with elevated triglycerides are likely to have higher-risk lipoprotein subclass profiles. Triglyceride-rich lipoproteins drive the metabolic reactions that produce LDL of abnormal size and cholesterol content. The quantities of these abnormal LDL particles and the associated risk of coronary heart disease are underestimated by conventional cholesterol measurements. Nuclear magnetic resonance spectroscopy measures lipoprotein subclasses directly and efficiently, and produces information that may improve the assessment and management of cardiovascular disease risk.